1. Field of the Invention
The present invention relates to a digital recording and playback apparatus adopting a moving picture experts group (MPEG) coder/decoder (CODEC), and a method therefor, and more particularly, to a digital recording and playback apparatus for a digital video camcorder, which is compatible with all apparatuses adopting the MPEG standard, in which an image signal is coded and decoded according to the MPEG-2 standard, and a method therefor.
2. Description of the Related Art
Following the MPEG-1 standard, the MPEG-2 standard has been introduced because of the need for a high quality picture at a higher bit rate. The MPEG-2 standard is applied in the broadcasting media field as well as the storage media field, and can provide quality higher than that provided by current analog television. Also, the MPEG-2 standard can be applied to a high definition television (HDTV). Thus, the MPEG-2 standard can be applied over a wide range, including telecommunication, home appliances, computers and broadcasting systems.
According to the trend for such high quality, an original standard for compression coding in a digital camcorder for recording and playing back a moving image was developed in Japan. However, this standard is not compatible with MPEG, and thus it is impossible to play back the coded data with a digital television or a multimedia system adopting the MPEG coding method, which will be widespread in the future.
Also, the HD digital video cassette recorder (VCR) conference was established in 1993, to suggest the basic specification of a digital video format and discuss the HDTV specification based on the basic standard. The HD-VCR Conference has decided on the standards for specifications of a standard definition (SD) format and a high definition (HD) format. The selected standards contemplate a rotary head scan method (helical scan), a compression method based on a discrete cosine transform (DCT), and a video tape having a width of ¼ inch for the basic specification. Also, according to a HD baseband format, the sampling frequency of the HDTV is set to 50.4 MHz, which is three times the sampling frequency (13.5 MHz) for SD, and a recording rate of video data is set to 50 Mbps, which is twice the recording rate (25 Mbps) for SD.
After the selection of an international standard for a next generation VCR and camcorder, a camcorder for SD has spread rapidly. In order to cope with the current trends, a digital television (DTV) using MPEG-2 and a digital video camcorder compatible with other applications are required.
Also, a digital television (DTV) working group (WG) for discussing formats for recording a DTV signal was established in the U.S. in 1994, and a digital video broadcasting (DVB) WG was established in Europe to discuss formats for recording a DVB signal.
When recording a DTV signal which has been compressed at a data rate of 19.3 Mbps on a video tape having an SD format, the signal is recorded at a video data rate of 25 Mbps for SD. When recording a DVB signal on a video tape having the SD format, by controlling the data rate of the DVB signal to be 10 Mbps or less, the recording is performed at 12.5 Mbps which is the half of the video data rate for SD, or at 6.25 Mbps which is a quarter of that for SD.
Because the DTV and DVB signals both adopt the compression coding method based on MPEG-2, a digital recording and playback apparatus having a format capable of recording the data compressed by the MPEG-2 method is required. However, because in MPEG-2 a high compression is performed in group of picture (GOP) units including a plurality of pictures, using correlation among those pictures, if the compressed data having this structure is simply recorded on a tape as it is, it is difficult to form the image during playback at multiple times speed (high-speed search), lowering the image quality.
In a conventional VCR, it is essential to edit the data in picture units and search at high-speed. Thus, the following method for achieving those functions has been introduced. For example, the video data rate for the SD format is 25 Mbps, while a DTV signal has a data rate of 19.3 Mbps, so the extra region corresponding to the difference between the compression rate and recording rate is used for high-speed search. That is, the data compressed by intra coding in GOP units is repeatedly recorded in a specific region of a video tape, so an image of a picture is constituted using the repeatedly recorded data, during playback at a multiple times speed.
When recording a DTV signal including data compressed by MPEG-2 at a rate of 19.3 Mbps and the compressed data is repeatedly recorded on a video tape, a high speed search (one of the main functions of a digital VCR) is possible. However, because the compression coding is performed in GOP units containing a plurality of pictures, it is impossible to edit the data in picture units, and the picture quality is lower than the SD data.
A conventional digital video camcorder for SD performs compression in picture units and independently in segment units having a predetermined number (in general, five) of macroblocks, so search in picture units and high-speed search can be performed. However, the conventional digital video camcorder is not compatible with apparatuses adopting the MPEG-2 standard.